Known wheel bearings of the type shown in FIGS. 1 and 2, and indicated generally at 10, have a stationary outer hub 12, which is secured to a non illustrated vehicle suspension, and a rotatable spindle, indicated generally at 14, with a central axis A shown by the dotted line. Spindle 14 carries two components that rotate with it, the vehicle wheel 16 and a brake drum 18. Brake drum 18 is mounted over spindle 14 through an open, flat circular hub 20, which has an annular inner edge 22 with a predetermined axial thickness T of approximately 7 to 8 mm. When the brake drum hub 20 is installed to spindle 14, its inner edge 22 is pushed axially over and guided along a cylindrical pilot surface 24, relative to which it has a very small radial clearance, as best seen in FIG. 2. A concentric, flat annular wheel flange 26 radiates outwardly from the pilot 24, perpendicular thereto, with a flat outer surface 28 against which the brake drum hub 20 is abutted. The brake drum hub 20 is firmly sandwiched between the flange surface 28 and the wheel 16 itself, which is bolted onto conventional studs 30 with non illustrated, conventional lug nuts. Similarly to brake drum 18, wheel 16 has a flat hub 32 with an annular inner edge 34 having a diameter and axial thickness similar to the drake drum hub inner edge 22. The wheel hub inner edge 34 guides over the pilot surface 24 in similar fashion with a comparable small radial clearance. The wheel hub 32 clamps the brake drum hub 20 against the flange surface 28 when the lug nuts are tightened down onto studs 30. After installation, the two hubs 20 and 32 are maintained concentric to axis A by the studs 30, so the pilot surface 24 with its close radial clearance is needed basically for guidance during installation (and removal) of the wheel 16 and brake drum 18, as its name implies, not for post installation concentricity support. However, the close radial clearance at the contact interface between the spindle pilot surface 24 and the two hub inner annular edges 22 and 34 remains after installation. During vehicle operation, that contact interface and its small radial clearance is exposed to water. The spindle 14 and brake drum 18 are invariably steel, and subject to corrosion or rusting, and the wheel 16 may be steel or aluminum, also subject to corrosion. After the wheel 16 and brake drum 18 have been installed for a long period, the respective annular edges 22 and 34 can essentially weld themselves to the pilot surface 24 because of corrosion growth at the contact interface, especially in environments exposed to salt water. This can make it difficult to remove and reinstall the wheel 16 or drum 18 for servicing.
A typical method for reducing corrosion at the contact interface is to simply coat the pilot surface 24 with a non corrosive paint or other coating. In addition to the obvious cost, such a layer can itself be scraped off with even a few removals and reinstallations, after which it would be ineffective. Whether coated or uncoated, spindle pilot surfaces known to have been used in actual production are cylindrical and basically smooth and uninterrupted, although they may have a stepped diameter to accommodate different diameter wheel and drum edges. However, an issued U.S. Pat. No. 5,080,500 to Hilby et al, shows a dual diameter cylindrical wheel bearing spindle pilot surface that appears to have been cut with conventional threads, for an unexplained purpose. It may be that the threads were used to attach a non corrosive sleeve, to insulate the wheel and brake drum edges from the pilot surface. This seems most likely, since sharp edged threads would retard the motion of a close fitting component edge sliding directly onto and over them, and would be easily marred and damaged in the process. Furthermore, direct contact (or small radial clearance) between a sharp edged thread and the annular inner edge of a brake drum or wheel hub would not likely be conducive to water corrosion reduction, as will be described further below.